A question I've never gotten a fully satisfying answer to: what mechanisms are kicking in to give me a 'second wind' late at night?Basically I go through my day (usually up around 7, in lab by 9) and am fairly exhausted by 8 or 9pm every night. But by 11pm/12am, my energy picks up again and I can easily work, exercise, whatever, until 3 or 4 in the morning before I start feeling tired again. Any thoughts on what causes the second wind?